1. Field of the Invention
The present invention relates to a semiconductor wafer cassette transportation apparatus and a stocker used in such a semiconductor wafer cassette transportation apparatus. More particularly, the present invention relates to a semiconductor wafer cassette transportation apparatus for improving the semiconductor wafer cassette transportation ability, and a stocker used in the semiconductor wafer cassette transportation apparatus.
2. Description of the Background Art
Referring to FIGS. 15 and 16, a conventional semiconductor wafer cassette transportation apparatus 230 includes processing apparatuses 32 and 34 receiving semiconductor wafers in the unit of a cassette 232 to apply a fabrication process of a semiconductor integrated circuit, a stocker 234 for storing a plurality of cassettes 232, an automatic carrier 38 for carrying out a transportation task of a cassette 232 between processing apparatus 32/34 and stocker 234, and an inter-stocker transport device 42 for conveying a cassette 232 between a plurality of stockers 234 arranged along the fabrication process line.
Processing apparatus 32/34 uses stocker 234 as a storage site of semiconductor wafer cassette 232 before and after the fabrication process. Two automatic carriers 38 are engaged in the transportation task of cassette 232 between processing apparatus 32/34 and stocker 234. For the sake of convenience, inter-stocker transport device 42 is indicated in a cut-off manner in the drawing. In practice, inter-stocker transport device 42 is arranged in a circulating manner with a plurality of stockers 234 disposed adjacent thereto. Respective groups of processing apparatus 32/34 and automatic carrier 38 correspond to each of other stockers 234.
Referring particularly to FIG. 16, semiconductor wafer cassette transportation apparatus 230 further includes a host computer 50 for controlling processing apparatuses 32 and 34, stocker 234, automatic carrier 38, and inter-stocker transport device 42, and a communication cable 58 for providing connection between various devices and host computer 50.
Host computer 50 includes a main body 52 to carry out a calculation process, a terminal 54 to enter fabrication standard data of a product, and a plurality of operator's terminals 56 provided at the line.
A stocker controller 64 which is an element of stocker 234 drives other structural elements of stocker 234 to carry out a predetermined task according to a task instruction from host computer 50 via communication cable 58. An automatic carrier controller 60 which is an element of automatic carrier 38 drives other structural elements of automatic carrier 38 to carry out a predetermined task according to a task instruction from host computer 50 via communication cable 58. Communication between automatic carrier controller 60 and automatic carrier 38 is carried out by radio via a control station communication unit 62. An inter-stocker transport device controller 66 which is an element of inter-stocker transport device 42 drives a structural element of inter-stocker transport device 42 and also a structural element of stocker 234 via communication cable 58 to carry out a predetermined task according to a task instruction sent from host computer 50 via communication cable 58.
Semiconductor wafer 70 and semiconductor wafer cassette 232 transferred by semiconductor wafer cassette transportation apparatus 230 and a conventional ID card 240 attached to semiconductor wafer cassette 232 will be described hereinafter with reference to FIGS. 17A-17C. A plurality of semiconductor integrated circuits (not shown) are produced on a semiconductor wafer (referred to as "wafer" hereinafter) 70. Semiconductor wafer cassette (referred to as "cassette" hereinafter) 232 is the minimum unit of storing and transporting a plurality of wafers 70. An ID card 240 is attached to cassette 232. ID card 240 includes information associated with cassette 232 and wafer 70 stored therein. Some of the information thereof can be provided on a display unit 74. ID card 240 can have the information partially rewritten via communication unit 76 with respect to an external control system that will be described afterwards. Also, the stored information can be reported in a non-contact manner. A communication unit 76 is attached at the front face of ID card 240. FIGS. 17A and 17B show a transversal orientation and a vertical orientation, respectively, of cassette 232 to which ID card 240 is attached. More specifically, in the transversal orientation, wafers 70 are stored with the disk plane in the vertical direction. In the vertical orientation, wafers 70 are stored with the disk plane in the horizontal direction. FIG. 17C shows ID card 240 in detail.
The details of processing apparatuses 32 and 34, stocker 234, automatic carrier 38, and inter-stocker transport device 42 will be described hereinafter with reference to the drawings.
Referring to FIG. 10, processing apparatus 32 includes a main body 170 for applying a semiconductor integrated circuit fabrication process on every one or a plurality of wafers 70, two cassette stages 172 receiving cassette 232 to be processed in the unit of one cassette, and a automatic carrier-directed communication unit 174 for providing information of the state of cassette stage 72 towards automatic carrier 38 to confirm whether any improper cassette 232 is mounted on cassette stage 172 before automatic carrier 38 places a cassette 232 not yet processed on cassette stage 172, or whether cassette 232 subjected to a process is properly mounted on cassette stage 172 before that cassette 232 is taken away.
Referring to FIG. 11, processing apparatus 34 includes a main body 180 for applying a semiconductor integrated circuit fabrication process on every one or a plurality of wafers 70, two cassette stages 182 receiving cassette 232 to be processed in the unit of 2 cassettes, and an automatic carrier-directed communication unit 174 for providing information of the state of cassette stage 182 towards automatic carrier 38 to confirm whether any improper cassette 232 is placed on cassette stage 182 before automatic carrier 38 places a cassette 232 to be processed on cassette stage 182, or whether cassette 232 subjected to a process is properly mounted on cassette stage 182 before that cassette 232 is to be taken away.
Stocker 234 will be described with reference to FIGS. 18-20. The operation side face of stocker 234 with respect to automatic carrier 38 and an opposite side face thereof are respectively shown in FIGS. 18 and 19. FIG. 20 shows in detail an inlet port 260 for manual input viewed from arrow A of FIG. 19. These figures are drawn with a stocker panel 94 which is the external panel partially cut away so that the interior can be shown. Stocker 234 includes a stocker shelf 96 on which a plurality of cassettes 232 can be mounted in transversal orientation. A storage site for a large number of cassettes 232 is acquired by stacking a plurality of cassettes 232 on respective stocker shelves 96 in the vertical direction. Stocker 234 includes a port 98 which is a portion of stocker shelf 96 and provided for the entry or exit of a cassette 232 conveyed by inter-stocker transport device 42, an inlet port 260 which is a portion of stocker shelf 96 and provided for an operator (not shown) to enter a cassette 232, an outlet port 262 which is a portion of stocker shelf 96 and provided for an operator to take away a cassette 232, an outlet port 252 for automatic carrier 38 to receive cassette 232, an outlet delivery port 100 which is a portion of stocker shelf 96 to transfer cassette 232 to outlet port 252, an inlet port 254 through which cassette 232 is input from automatic carrier 38, an inlet delivery port 104 which is a portion of stocker shelf 96 and on which cassette 232 from inlet port 254 is placed, a stocker crane 80 arranged between stocker shelves 96 for the transportation task of cassette 232 between a cassette storage site on stocker shelf 96 and respective ports of stocker shelf 96, a transfer device 82 for receiving cassette 232 from the carriage of inter-stocker transport device 42 and placing the same on port 98, or for providing cassette 232 from port 98 onto an empty carriage of inter-stocker transport device 42, and a forward translate device 250 for transferring cassette 232 from port 100 to port 252, or from port 254 to port 104.
Stocker crane 80, transfer device 82, and forward translate device 250 carry out a transportation task in the unit of 1 cassette, 2 cassettes, and 1 cassette, respectively. The number of cassettes that can be mounted at port 98, inlet port 260, outlet port 262, outlet delivery port 100, inlet delivery port 104, outlet port 252 and inlet port 254 is 2 cassettes, 1 cassette, 1 cassette, 1 cassette, 1 cassette, 1 cassette, and 1 cassette, respectively. Two forward translate devices 250 are provided. Accordingly, two outlet ports 252, two inlet ports 254, two outlet delivery ports 100, and two inlet delivery ports 104 are provided. Also, two inlet ports 260 and two outlet ports 262 for manual input/output are provided.
As shown in FIG. 20, an ID card reader/writer 270 is attached at each inlet port 260. Since ID card communication unit 76 is located at the front face of ID card 240, ID card reader/writer 270 must be provided corresponding to the front face of ID card 240. If ID card reader/writer 270 is disposed so that the front face of ID card 240 faces the operation plane side of the operator, cassette 232 cannot be easily output due to the obstacle of ID card reader/writer 270. Therefore, cassette 232 on inlet port 260 for manual input is oriented so that the front face of ID card 240 attached to cassette 232 is 90.degree. rightwards with respect to the operation plane side of the operator. Since stocker crane 80 cannot modify the orientation of cassette 232, the orientation of cassette 232 on stocker shelf 96 is identical to that of cassette 232 on inlet port 260. However, the orientation of cassette 232 placed at outlet port 252 and inlet port 254 is arranged so that ID card 240 directly faces the task plane for automatic carrier 38 to facilitate the transfer. Therefore, forward translate device 250 must also alter the orientation of cassette 232 during the transfer.
Stocker 234 further includes an operation panel 121 used by the operator during entry/exit of cassette 232 through inlet port 260/outlet port 262.
Referring to FIG. 8, automatic carrier 38 includes a carriage 140 that runs according to the guidance of a guide tape 156 that is affixed to the floor, a carrier communication unit 142 for transferring information to and from control station communication unit 62 of automatic carrier controller 60, an arm 144, a hand 146, and a hand claw 148 for performing a carry task of cassette 232, four transfer mounts 150 for maintaining cassette 40 taken from processing apparatus 32/34 or from stocker 234 in the vertical orientation during travel, an operation panel 152 to transfer information to and from the operator, and a bumper 154 for detecting an obstacle to cease the current task.
Referring to FIG. 9, inter-stocker transport device 42 includes a travel rail 160 forming a loop, a carriage 162 moving in a constant direction on travel rail 160 for conveying not more than two cassettes 40, and a pendant 232 for hanging travel rail 160 from the ceiling.
A conventional method of controlling semiconductor wafer cassette transportation apparatus 230 will be described hereinafter. First, (1) the control method of a processed cassette 232 from processing apparatus 32/34 being carried by automatic carrier 38 into stocker 234, and then conveyed by inter-stocker transport device 42 to the next stocker 234 will be described. Then, (2) the control method of a cassette 232 to be processed being carried from a stocker 234 of the preceding stage into a stocker 234, and then output therefrom according to a request from processing apparatus 32/34 to be carried thereto by automatic carrier 38 will be described. Finally, (3) the control method of entry through inlet port 260 for manual input and exit through outlet port 262 for manual output will be described.
Control Method (1)
Automatic carrier related inlet port 254 and for inter-stocker transport device related port 98 are both empty when the power of stocker 234 is turned on and initialization is completed. A report is provided to host computer 50 via communication cable 58 that each port can receive a cassette 232. Upon receiving the port available information, host computer 50 determines whether the transportation task of cassette 232 into stocker 234 using automatic carrier 38 and inter-stocker transport device 42 is possible or not by the received port available information without detecting the stock status of cassette 232 in stocker 234.
Under the above state, processing apparatus 32/34 sends to host computer 50 via communication cable 58 a hand-over request of processed cassette 232 subjected to the semiconductor integrated circuit fabrication process. Processing apparatus 32/34 requests the cassette to be handed over in the unit of one cassette or in the unit of a plurality of cassettes. In response to this hand-over request, host computer 50 provides a transportation task instruction immediately to automatic carrier 38 via communication cable 58 since the available information of inlet port 254 for automatic carrier 38 is reported from stocker 234 in advance. The available inlet port 254 is determined corresponding to each of processing apparatuses 32 and 34. The data thereof is provided to host computer 50 in advance through terminal 54. Host computer 50 must send a transportation task instruction in the unit of 1 cassette to automatic carrier 38 even when a hand-over request in the unit of 2 cassettes is provided from processing apparatus 32/34 since entry of a cassette through inlet port 254 is carried out only by 1 cassette at a time.
Automatic carrier controller 60 receiving the transportation task instruction of one cassette from host computer 50 assigns the task to the most appropriate one of the plurality of automatic carriers 38 so as to execute a transportation task by communication with the main body through radio by means of control station communication unit 62 and carrier communication unit 142. This transportation task is set forth in the following. First, carriage 140 heads for processing apparatus 32/34 from which a cassette is to be unloaded, i.e., the source of transportation (referred to as "source" hereinafter) according to guide tape 152 affixed to the floor at the standby site. At the site of processing apparatus 32/34, automatic carrier 38 confirms whether there is a cassette 232 at the relevant cassette stage 172/182 via automatic carrier-directed communication unit 174. Then, arm 144, hand 146 and hand claw 148 are driven to take and place onto transfer mount 150 a relevant cassette 232 from cassette stage 172/182. Following this mounting task, carriage 140 moves from the site of source processing apparatus 32/34 towards a designated inlet port 254 of a stocker 234 to which a cassette is to be loaded, i.e., the destination of transportation (referred to as "destination" hereinafter).
Arriving at the destination stocker 234, automatic carrier 38 places cassette 232 on transfer mount 150 onto inlet port 254 in a sequence opposite to that described above. Before placing cassette 232 at the designated inlet port 254, automatic carrier 38 confirms whether there is no improper cassette 232 at inlet port 254 via carrier-directed communication unit 102 and immediately issues an error when there is an improper cassette 232. This error is based on the determination that another cassette 232 on the same port implies an abnormal state since cassette 232 is carried according to the empty information of inlet port 254 from stocker 234. When all the designated tasks are completed, automatic carrier controller 60 sends a task complete report to host computer 50 via communication cable 58.
Upon receiving a task complete report from automatic carrier 38, host computer 50 sends to stocker 234 an entry task instruction of cassette 232 through inlet port 254. In response to this entry task instruction sent via communication cable 58, stocker controller 64 ascertains a storage site on stocker shelf 96 and then initiates the task. When a storage site cannot be ascertained, stocker controller 64 waits for the vacancy of a storage site without initiating the task. Stocker 234 commencing an entry task drives forward translate device 250 to rotate cassette 232 90.degree., which is then moved from inlet port 254 to inlet delivery port 104. When this transfer task is completed, stocker crane 80 is actuated to carry cassette 232 on inlet delivery port 104 to the storage site on stocker shelf 96 ascertained by stocker controller 64. Thus, the series of an entry task is completed. Upon completion of this task, stocker controller 64 provides a task complete report to host computer 50 via communication cable 58. When inlet port 254 becomes available during the transfer task from inlet port 254 to inlet delivery port 104, stocker 234 provides this port empty information to host computer 50 analogous to the time of initialization, to prepare for the next transportation task using automatic carrier 38.
Host computer 50 receiving an entry task complete report from stocker 234 determines the destination stocker 234 for that cassette 232. Also, confirmation is carried out whether port 98 for inter-stocker transport device 42 of the destination stocker 234 is empty or not. This port empty information is sent to host computer 50 when initialization is completed at the turn-on of stocker 234 or when the relevant port becomes available. When port 98 of destination stocker 234 is empty, host computer 50 sends a transportation task instruction of cassette 232 associated with source stocker 234 to inter-stocker transport device 42 via communication cable 58. In response, inter-stocker transport device controller 66 provides a transfer task request of cassette 232 from the storage site towards port 98 in source stocker 234 via communication cable 58. Stocker 234 that is assigned to the transfer task moves cassette 232 using stocker crane 80. Then, a task complete report is sent to inter-stocker transport device controller 66. In response, inter-stocker transport device controller 66 despatches an empty carriage 162 to a station corresponding to source stocker 234. After this movement, inter-stocker transport device controller 66 provides a request to source stocker 234 so that the relevant cassette 232 on port 98 is moved towards empty carriage 162. Stocker 234 assigned to that request moves cassette 232 through transfer device 82. Then, a task complete report is sent to inter-stocker transport device controller 66. Inter-stocker transport device controller 66 receiving this task complete report moves carriage 162 to the station corresponding to destination stocker 234. Thus, a cassette 232 processed by processing apparatus 32/34 is carried and entered into stocker 234 by automatic carrier 38, and then output by inter-stocker transport device 42 to be sent to the next stocker 234 while the transportation task between stockers is continued.
Control method (2)
By sending the empty information of port 98 of destination stocker 234 from stocker controller 64 to host computer 50 via communication cable 58, a new cassette 232 to be processed is placed on carriage 162 to be transferred to destination stocker 234. At the arrival of carriage 162, inter-stocker transport device controller 66 sends via communication cable 58 a request to stocker controller 64 so that cassette 232 on carriage 162 is placed on port 98. Stocker 234 assigned to this request carries out the task using transfer device 82. Then, a task complete report is sent to inter-stocker transport device controller 66.
In response, inter-stocker transport device 66 sends a report that the task is completed. Host computer 50 receiving this report sends an instruction to destination stocker 234 to enter cassette 232 on port 98. According to the entry task instruction sent via communication cable 58, stocker controller 64 ascertains a storage site on stocker shelf 96 and then initiates the task. When a storage site cannot be ascertained, stocker controller 64 will not initiate the task, and waits for a storage site to become available. Stocker 234 commencing the entry task moves cassette 232 on port 98 to the ascertained storage site on stocker shelf 96 using stocker crane 80. When the instructed task is completed, stocker 234 sends a task complete report to host computer 50. Cassette 232 to be processed that is stored in stocker 234 is left there to wait for cassette stage 172/182 of processing apparatus 32/34 of the subsequent process to become available.
A cassette load request from processing apparatus 32/34 is sent to host computer 50 via communication cable 58 in a state where cassette 232 to be processed is stored in stocker 234. Host computer 50 identifies whether there is a cassette 232 to be processed in stocker 234, and proceeds to an exit task when there is an appropriate cassette. When there is no cassette 232, host computer 50 waits for an appropriate cassette 232 to be entered into stocker 234. Processing apparatus 32/34 may send a load request of a plurality of cassettes 232 at one time according to the type thereof. Since only one cassette 232 can be placed at outlet port 252, the exit task from stocker 234 and the transportation task from stocker 234 to processing apparatus 32/34 corresponding to a request of a plurality of cassettes are repeatedly carried out for the number of the cassettes.
Host computer 50 in the exit task phase selects one of the plurality of output ports 252 according to processing apparatuses 32/34 sending the entry request. Also, an exit task instruction of cassette 232 thereto is sent to source stocker 234 via communication cable 58. The available outlet port 252 is determined according to each of processing apparatuses 32 and 34, similar to inlet port 254. The data thereof is applied to host computer 50 in advance via terminal 54. Stocker 234 receiving the exit task instruction transfers the relevant cassette 232 to outlet delivery port 100 using stocker crane 80. Then, stocker 234 drives forward translate device 250 to forward cassette 232 on outlet delivery port 100 to outlet port 252. Furthermore, cassette 232 is rotated 90.degree. to facilitate the operation of automatic carrier 38. Thus, the exit task to outlet port 252 is completed. Stocker 234 sends a task complete report to host computer 50.
Host computer 50 receiving the exit task complete report from stocker 234 sends an instruction to automatic carrier 38 via communication cable 58 so that cassette 232 on outlet port 252 is carried to cassette stage 172/182 of destination processing apparatus 32/34. Automatic carrier controller 60 receiving this instruction assigns the most appropriate one of the plurality of automatic carriers 38 to the transportation task, whereby that automatic carrier 38 carries out a transportation task of cassette 232 by communication with the main body via radio using control station communication unit 62 and carrier communication unit 142.
This transportation task will be described hereinafter. Carriage 140 of automatic carrier 38 at the standby site moves towards outlet port 252 of stocker 234 according to guide tape 156 affixed to the floor. When arriving at source stocker 234, automatic carrier 38 confirms whether there is a cassette 232 at outlet port 252 via carrier-directed communication unit 102. Then, automatic carrier 38 drives arm 144, hand 142 and hand claw 148 to fetch and place on transfer mount 150 cassette 232 from outlet port 252. When cassette 232 is missing as a result of confirmation, an error is immediately issued. Following the mounting task, carriage 140 moves from stocker 234 to the front of a designated cassette stage 172/182 of destination processing apparatus 32/34. Automatic carrier 38 places cassette 232 on cassette stage 172/182 from mount 150 according to a procedure opposite to that of the above sequence. Before placing cassette 232 on the designated cassette stage 172/182, automatic carrier confirms whether there is no improper cassette 232 on cassette stage 172/182 via carrier-directed communication unit 174. An error is immediately issued when there is an improper cassette 232. This error is based on the determination that another cassette 232 on the relevant cassette stage implies an improper state since cassette 232 is carried according to the empty information of cassette stage 172/182 from processing apparatus 32/34. When all the designated tasks are completed, automatic carrier controller 60 provides a task complete report to host computer 50 via communication cable 58.
Following the loading task of cassette 232 into processing apparatus 32/34 by automatic carrier 38, host computer 50 sends a predetermined process initiation instruction to processing apparatus 32/34 via communication cable 58.
Control Method (3)
When cassette 232 is to be entered into stocker 234 in a manual manner, the operator first places cassette 232 at inlet port 260 and operates operation panel 121 which is provided integral with stocker 234. The operation by panel 121 allows stocker 234 to detect that cassette 232 has been placed at inlet port 260. The information on ID card 240 of that cassette 232 is read by ID card reader/writer 270. The data read out is sent to host computer 50 through communication cable 58. Host computer 50 becomes aware that the operator has placed a cassette 232 by this report. Host computer 50 sends an input task instruction of cassette 232 to stocker 234 without checking the stock status of cassette 232 in stocker 234. The available inlet port 260 is determined corresponding to processing apparatuses 32/34. The data thereof is applied in advance to host computer 50 via terminal 54. According to the entry task instruction provided via communication cable 58, stocker controller 64 ascertains a storage site on stocker shelf 96, and then initiates the task. When a storage site cannot be ascertained, stocker controller 64 will not initiate the task and waits for a storage site to become available. Stocker 234 initiating the entry task instruction transfers cassette 232 on inlet port 260 onto the storage site on stocker shelf 96 using stocker crane 80. When this task is completed, stocker 234 sends a task complete report to host computer 50. Thus, the entry task by an operator is completed.
The method of unloading cassette 232 stored in stocker 234 through outlet port 262 for an operator will be described hereinafter. Consider the case where a cassette is to be loaded to processing apparatus 32/34 from source stocker 234 when automatic carrier 38 is not provided. Processing apparatus 32/34 sends a cassette load request to host computer 50 via communication cable 58. Host computer 50 identifies whether there is a cassette 232 to be processed in stocker 234. When there is a cassette to be processed, host computer 50 proceeds to the exit task phase. When there is no cassette, computer 50 waits for entry of a relevant cassette to be processed into stocker 234. Processing apparatus 32/34 may send a load request of a plurality of cassettes 232 at one time according to the type thereof. When a request of a plurality of cassettes is provided, the exit task from stocker 234 which will be described afterwards will be carried out repeatedly for a number of times corresponding to the number of the requested cassettes.
Host computer 50 in the exit task phase selects any of the plurality of outlet ports 262 according to processing apparatuses 32/34 providing the load request. An exit task instruction associated with the selected outlet port 262 is sent to source stocker 234 via communication cable 58. The available outlet port 262 for manual output is determined depending on each of processing apparatuses 32 and 34, similar to outlet port 252 for the automatic carrier. The data is applied to host computer 50 in advance via terminal 54. The relevant stocker 234 transfers cassette 232 to outlet port 262 using stocker crane 80. Also, a display is provided on operation panel 121 of stocker 234 permitting the operator to take away cassette 232 on outlet port 262. In response to this display, the operator outputs cassette 232 from outlet port 262 and notifies that the take out task is completed to stocker 234 via operation panel 121. In response, stocker 234 determines that the exit task is completed. A complete report thereof is sent to host computer 50 via communication cable 58. The operator unloading cassette 232 must carry that cassette to cassette stage 172/182 of the appropriate processing apparatus 32/34 that issued the load request. However, the operator does not know which processing apparatus 32/34 has issued the request. The operator must use operator's terminal 56 of host computer 50 to identify the appropriate processing apparatus 32/34. Then, the operator carries cassette 232 to the identified appropriate processing apparatus 32/34 and places it on cassette stage 172/182.
The above-described conventional semiconductor wafer cassette transportation apparatus 230 has problems set forth in the following.
When the number of cassettes requested to be handed over from processing apparatus 32/34 is greater than the number of cassettes that can be mounted at automatic carrier related inlet port 254, the remaining processed cassettes exceeding the mountable number of cassettes will be left on cassette stage 172/182 of processing apparatus 32/34. The period of time of cassette 232 left on cassette stage 172/182 in the standby state for a transportation task is increased. Also, the vacancy of cassette stage 172/182 is delayed. This means the time required for supplying a cassette to be processed to processing apparatus 32/34 is increased.
Stocker 234 communicates with the ambient environment through automatic carrier related inlet delivery port 104, automatic carrier related outlet delivery port 100, inter-stocker device related port 98, inlet port 260 for manual input, and outlet port 262 for manual output. There is a possibility that dust and mist will enter stocker 234 to be attached to wafer 70 in cassette 232 through these ports. Wafer 70 can be adversely affected by the dust and mist.
The orientation of cassette 232 on inlet port 254 in stocker 234 differs from the orientation of cassette 232 on inlet delivery port 104 by 900. Therefore, cassette 232 must be rotated during the task carried out by forward translate device 250.
When the number of cassettes by processing apparatus 32/34 requested to be loaded is greater than the number of cassettes that can be mounted on outlet port 252, any cassette 232 exceeding the mountable number of cassettes will be deferred for a subsequent transportation task. Therefore, the preceding cassette 232 already arriving at cassette stage 172/182 of processing apparatus 32/34 cannot be processed by processing apparatus 32/34 and has to wait until a succeeding cassette 232 arrives.
The orientation of cassette 232 on outlet port 252 differs 90.degree. from the orientation of cassette 232 on outlet delivery port 100. Therefore, cassette 232 must be rotated during the task carried out by forward translate device 250.
ID card 240 of cassette 232 placed on inlet port 260 and outlet port 262 does not face the operation plane side of the operator. The operator had difficulty in confirming the cassette 232 placed on port 260/262.
Inlet port 260 for manual input that can be used is determined according to each processing apparatus 32/34. When there are a plurality of inlet ports 260, there will be variation in the usage and occupancy of inlet port 260 depending upon the processing ability and operation state of each of processing apparatuses 32/34.
When the number of cassettes requested by processing apparatus 32/34 to be loaded is greater than the number of cassettes that can be mounted on outlet port 262, any cassette exceeding the number of mountable cassettes will be deferred for a subsequent exit task. Therefore, the workability of the operator is degraded.
The operator does not know which processing apparatus 32/34 the cassette 232 taken away manually from outlet port 262 is to be carried to. The operator must approach terminal 56 of host computer 50 to obtain the information to identify the appropriate processing apparatus 32/34. Therefore, the time required for the task is increased.